Centrifugal compressors generally consist of at least two main components: an impeller and a diffuser. As the fluid flowing from the impeller of the compressor to the diffuser is reduced, the incidence of the flow on the diffuser vanes and the static pressure within the diffuser passages increases, until stall eventually results within the passages, followed by stage “surge”. Surge of the compressor is a well know problem, and therefore many means for controlling and/or delaying the onset of surge have been attempted in the past, however none have been found to be ideal. As such, there continues to be a need for improvement in this regard.